Ink jet recording device

Abstract

To provide an ink jet recording device capable of suppressing deterioration of image quality.SOLUTION: In an ink jet recording device, during execution of a correction mode, a control unit causes an image reading unit to read a check chart for density measurement that has been recorded on a sheet by a recording unit, thereby acquiring density information of a recording head. The ink jet recording device repeatedly corrects driving conditions of the recording head until the acquired density information of the recording head becomes equal to or less than a predetermined threshold. The ink jet recording device determines whether or not the density information of the recording head has converged toward a predetermined value each time the driving conditions are corrected when the driving conditions of the recording head have been corrected a predetermined number of times, and changes the threshold when the density information of the recording head has not converged toward the predetermined value.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording apparatus. [Background technology]

[0002] A conventional inkjet recording device includes a recording unit, an image reading unit, and a control unit. The recording unit ejects ink from multiple nozzles of multiple recording heads to record an image on a sheet. The image reading unit reads the density of the image recorded on the sheet. The control unit controls the recording unit and the image reading unit.

[0003] The control unit acquires density information of the print head by reading the density measurement check chart printed on the sheet by the printing unit using the image reading unit. The control unit also corrects the drive conditions of the print head based on the acquired density information of the print head. This adjusts the ink ejection amount of the print head, thereby suppressing density unevenness in the image printed on the sheet. This also suppresses degradation of image quality due to density unevenness. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-81344 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the conventional inkjet recording device disclosed in Patent Document 1, when a check chart is recorded on a sheet of varying quality, such as recycled paper, there is a possibility that density unevenness in the check pattern will vary from sheet to sheet. As a result, the acquired density information of the recording head may also vary from sheet to sheet. As a result, when the drive conditions of the recording head are corrected, there is a possibility that density unevenness will not be eliminated and image quality will deteriorate.

[0006] The present invention has been made in view of the above points, and has as its object to provide an inkjet recording apparatus that can suppress deterioration in image quality. [Means for solving the problem]

[0007] In order to solve the above problems, the inkjet recording apparatus of the present invention includes a recording unit, an image reading unit, and a control unit. The recording unit ejects ink from a plurality of nozzles of a plurality of recording heads to record an image on a sheet. The image reading unit reads the density of the image recorded on the sheet. The control unit controls the recording unit and the image reading unit. The control unit is capable of executing a correction mode that corrects the drive conditions of the recording heads when a normal image formation mode is being executed. When the correction mode is executed, the control unit acquires density information of the recording heads by having the image reading unit read a check chart for density measurement recorded on the sheet by the recording unit. The control unit also repeatedly corrects the drive conditions of the recording heads until the acquired density information of the recording heads becomes equal to or less than a predetermined threshold. When the drive conditions of the recording heads have been corrected a predetermined number of times, the control unit determines whether the density information of the recording heads has converged toward a predetermined value each time the drive conditions of the recording heads are corrected, and if the density information of the recording heads has not converged toward the predetermined value, changes the threshold. [Effects of the Invention]

[0008] According to the configuration of the present invention, it is possible to provide an inkjet recording apparatus that can suppress deterioration in image quality. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an inkjet recording apparatus 100 according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the recording unit 104 of the inkjet recording apparatus 100 of FIG. [Figure 3] 1 is a block diagram of an inkjet recording apparatus 100 according to an embodiment of the present invention. [Figure 4]1 is a plan view showing an example of a check chart 20 for measuring concentration according to an embodiment of the present invention. [Figure 5] 5 is a flowchart showing an example of execution of a correction mode in the inkjet recording apparatus 100 according to an embodiment of the present invention. [Figure 6] 10 is a graph showing the relationship between the number of times the driving conditions of the print head 104 are corrected and density unevenness. [Figure 7] 10 is a graph showing the relationship between the number of times the driving conditions of the print head 104 are corrected and density unevenness. [Figure 8] 10 is a graph showing the relationship between the number of times the driving conditions of the print head 104 are corrected and density unevenness. DETAILED DESCRIPTION OF THE INVENTION

[0010] <1. Configuration of Inkjet Recording Apparatus> Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view showing a schematic configuration of an inkjet recording apparatus 100 to which a method for detecting density unevenness in nozzles according to an embodiment of the present invention is applied. Fig. 2 is a plan view of a recording unit 104 of the inkjet recording apparatus 100 shown in Fig. 1.

[0011] The inkjet recording apparatus 100 is, for example, an inkjet recording printer. The inkjet recording apparatus 100 includes a main body (apparatus main body) 101, a sheet supply unit 102, a sheet conveying unit 103, a recording unit 104, a drying unit 105, a sheet discharge unit 106, and a control unit 107.

[0012] The sheet supply unit 102 stores multiple sheets (recording media) P and separates and sends out the sheets P one by one during recording. The sheet supply unit 102 includes a cassette CA. The cassette CA stores the sheets P. That is, the inkjet recording apparatus 100 is equipped with the sheet supply unit 102 including the cassette CA that stores the sheets P. The cassette CA is detachable from the main body 101. The operation of storing the sheets P in the cassette CA is performed by the user. When performing the storage operation, the user pulls out the cassette CA from the main body 101, stores the sheets P in the cassette CA, and then attaches the cassette CA to the main body 101.

[0013] The sheet conveying unit 103 conveys the sheet P sent out from the sheet supply unit 102 to the recording unit 104 and the drying unit 105, and further discharges the sheet P after printing and drying to the sheet discharge unit 106. The sheet conveying unit 103 has a first belt conveying unit 1031 and a second belt conveying unit 1032. The first belt conveying unit 1031 and the second belt conveying unit 1032 adsorb and hold the sheet P on the upper surface of an endless belt and convey it. When double-sided printing is performed, the sheet conveying unit 103 distributes the sheet P after printing and drying on the first side to the reversing conveying unit 1034 by the branching unit 1033, and further switches the conveying direction to reverse the sheet P and convey it again to the recording unit 104 and the drying unit 105.

[0014] The recording unit 104 faces the sheet P, which is attracted to and held on the upper surface of the first belt conveyor 1031 and conveyed, and is disposed above the first belt conveyor 1031 at a predetermined distance. The recording unit 104 has, for example, line-type inkjet recording heads 1041. The recording heads 1041 include recording heads 1041B, 1041C, 1041M, and 1041Y corresponding to four colors: black, cyan, magenta, and yellow. A plurality (e.g., three) of the recording heads 1041 for each color are arranged in a staggered pattern along the sheet width direction (arrow Dm in FIG. 2 = main scanning direction) perpendicular to the sheet conveyance direction (arrow Ds in FIG. 2 = sub-scanning direction). The number and arrangement of the recording heads 1041 are not limited to the example described above.

[0015] The multiple nozzles 1042 are arranged in a row along the sheet width direction (main scanning direction) Dm, and can eject ink over the entire printing area. The printing unit 104 sequentially ejects ink from four color printing heads 1041B, 1041C, 1041M, and 1041Y toward the sheet P conveyed by the first belt conveying unit 1031, and records a full-color image or a monochrome image on the sheet P.

[0016] More specifically, the print head 1041 is an inkjet head having a plurality of print elements including a plurality of nozzles 1042. The nozzles 1042 are arranged at the bottom of the print head 1041.

[0017] In addition to the nozzles 1042, the recording elements include pressure chambers (not shown) that store ink and piezoelectric elements (not shown) that are provided on the side walls of the pressure chambers, and the pressure chambers communicate with the nozzles 1042. The recording head 1041 is supplied with a driving voltage as a driving condition from the control unit 107 that causes the piezoelectric elements to deform in accordance with the pixel values ​​of the image data.

[0018] This causes the piezoelectric element to deform, and the pressure chamber deforms in response to the drive voltage from the recording head 1041. At this time, the pressure inside the pressure chamber changes, and ink is ejected from the nozzles 1042 that communicate with the pressure chamber. As a result, from each of the nozzles 1042, a liquid amount of ink corresponding to the pixel value of the image data is ejected toward the sheet P, and an image is formed on the sheet P.

[0019] The drying unit 105 is disposed downstream of the recording unit 104 in the sheet conveying direction, and is provided with a second belt conveying unit 1032. The sheet P on which an ink image has been recorded in the recording unit 104 is adsorbed and held by the second belt conveying unit 1032 in the drying unit 105, and the ink is dried while being conveyed.

[0020] The control unit 107 includes a CPU, a memory unit, and other electronic circuits and electronic components (not shown). The CPU controls the operation of each component provided in the inkjet recording apparatus 100 based on control programs and data stored in the memory unit to perform processing related to the functions of the inkjet recording apparatus 100. The sheet supply unit 102, the sheet conveying unit 103, the recording unit 104, and the drying unit 105 each receive individual commands from the control unit 107 and perform recording on the sheet P in cooperation with each other. The memory unit is configured by a combination of a non-volatile storage device such as a program ROM (Read Only Memory) or a data ROM (not shown), and a volatile storage device such as a RAM (Random Access Memory).

[0021] 3 is a reading area diagram showing a schematic configuration of the inkjet recording apparatus 100. The inkjet recording apparatus 100 further includes a display unit 2, an operation unit 3, and an image reading unit 4. The density unevenness detection unit 1 can execute various processes for detecting density unevenness of the nozzles 1042. The display unit 2, the operation unit 3, and the image reading unit 4 are connected to a control unit 107.

[0022] The display unit 2 is configured, for example, by a liquid crystal display panel or the like, and can display various information related to the control unit 107, information about processing results, etc. The operation unit 3 is an input device configured, for example, by a keyboard, a touch panel, etc., and can input operation information, setting information, etc. to the control unit 107.

[0023] The image reading unit 4 includes an image sensor such as a line sensor, optically reads the image on the sheet P, generates image data corresponding to the image, and transmits the image data to the control unit 107. The control unit 107 executes various processes for detecting density unevenness of the nozzles 1042 based on the image data of the check chart 20.

[0024] The image sensor has, for example, a plurality of detection elements 41, a light source, a lens, etc. The detection elements 41 are a plurality of photoelectric conversion elements arranged in the sheet width direction, with approximately the same number of detection elements 41 corresponding to the plurality of nozzles 1042. The image reading unit 4 detects ink ejected onto the sheet P by receiving reflected light from the light source irradiated onto the sheet P via the lens at the detection elements 41.

[0025] The image reading unit 4 can acquire the image of the sheet P on which the check chart 20 is recorded, for each of a plurality of wavelength components, for example, three wavelengths of red (R), green (G), and blue (B). The detection element of the line sensor can be a CCD (Charge Coupled Device) type imaging element or a CMOS (Complementary Metal Oxide Semiconductor) type imaging element. The image reading unit 4 is not limited to the above configuration; for example, an area sensor in which imaging elements are arranged two-dimensionally can be used instead of the line sensor. In this embodiment, the image reading unit 4 measures the color of the image of the sheet P based on RGB values, but color measurement can also be based on Lab values.

[0026] The control unit 107 controls the printing operation by the multiple nozzles 1042. The control unit 107 includes a density information acquisition unit 1075, a determination unit 1077, an image processing unit 1071, a discharge control unit 1072, and a correction unit 1073. The functions of each of these components are realized by performing arithmetic processing in accordance with a predetermined program.

[0027] The density information acquisition unit 1075 acquires the density values ​​of the check chart 20 based on the image data acquired from the image reading unit 4. In addition, the density information of the recording head 1041 corresponding to the check chart 20 is acquired based on the acquired density values.

[0028] The determination unit 1077 determines the density information of the print head 1041 acquired by the density information acquisition unit 1075 using a threshold value stored in advance in a storage unit. This makes it possible to determine whether density unevenness has occurred in a part of the check chart 20. If the determination unit 1077 determines that density unevenness has occurred in a part of the check chart 20, it identifies the nozzle 1042 that is causing the density unevenness from the result of the determination.

[0029] The image processing unit 1071 generates recording data to be actually recorded on the sheet P based on the image data for recording input to the inkjet recording apparatus 100. Furthermore, when the correction mode is executed and the nozzle 1042 causing the density unevenness is identified, the image processing unit 1071 generates recording data to record the check chart 20 for density measurement on the sheet P.

[0030] The ejection control unit 1072 controls the ink ejection operation of each of the multiple nozzles 1042 so that an image corresponding to the print data generated by the image processing unit 1071 is recorded on the sheet P. More specifically, the ejection control unit 1072 controls the drive voltage to the print head 1041 based on the set drive conditions of the print head 1041, thereby controlling the ejection amount of ink droplets ejected from each of the nozzles 1042.

[0031] The correction unit 1073 executes various correction processes when the determination unit 1077 identifies an abnormal nozzle 1042. For example, the correction unit 1073 receives information from the determination unit 1077 that density unevenness has occurred in a part of the check chart 20 and density information about the print head 1041 that is causing the density unevenness. The correction unit 1073 corrects the driving conditions of the print head 1041 that is causing the density unevenness based on the density information. This increases or decreases the amount of ink droplets ejected from each nozzle 1042 of the print head 1041 that is causing the density unevenness, thereby suppressing the occurrence of density unevenness.

[0032] The driving conditions of the recording head 1041 include, for example, the magnitude of the voltage value (voltage amplitude) or application time of the driving voltage applied to the recording head 1041. By correcting the driving conditions of the recording head 1041, it is possible to adjust the amount of ink droplets ejected from each nozzle 1042. The ink ejected from the nozzles 1042 may be a hot-melt ink composition made of a material such as wax that is solid at room temperature, or a phase-change ink composition that changes phase to a gel state on the recording medium.

[0033] 5 is a plan view showing an example of a check chart 20 for detecting density unevenness according to an embodiment. In FIG. 5, reading areas 22Y, 22B, 22C, and 22M are indicated by dashed lines. Note that the identification symbols "B," "C," "M," and "Y" representing each color may be omitted unless otherwise specified.

[0034] The check chart 20 includes check patterns 21Y, 21B, 21C, and 21M drawn with ink droplets of yellow, black, cyan, and magenta, respectively.

[0035] In this embodiment, the check patterns 21Y, 21B, 21C, and 21M are halftone patterns, each of which is a band-shaped pattern having a predetermined length in the sub-scanning direction Ds and extending across the entire area in the main scanning direction Dm. Fig. 5 shows an example in which the check patterns 21Y, 21B, 21C, and 21M are arranged in the order of yellow (21Y), black (21B), cyan (21C), and magenta (21M) from the upstream side in the sub-scanning direction, but the present invention is not limited to this order.

[0036] The check patterns 21Y, 21B, 21C, and 21M are each divided into a plurality of reading areas 22Y, 22B, 22C, and 22M aligned in the main scanning direction Dm. The reading areas 22Y, 22B, 22C, and 22M are used to determine whether the density information of the print head 1041 is converging toward a predetermined value each time the drive conditions of the print head 1041 are corrected.

[0037] In this embodiment, 12 reading areas 22Y, 22B, 22C, and 22M are arranged in the main scanning direction Dm. Each of the reading areas 22Y, 22B, 22C, and 22M is square and made up of a plurality of pixels (nozzles 1042).

[0038] For check patterns 21Y, 21B, 21C, and 21M, the density values ​​are measured for each of reading areas 22Y, 22B, 22C, and 22M aligned in the main scanning direction Dm. The density values ​​are also measured each time the drive conditions of the print head 1041 are corrected. By comparing the acquired density values, it is possible to determine whether the density values ​​are converging toward a predetermined value each time the drive conditions of the print head 1041 are corrected. In other words, by comparing the acquired density values, it is possible to determine whether the density information of the print head 1041 is converging toward a predetermined value each time the drive conditions of the print head 1041 are corrected.

[0039] In this embodiment, density information of the print head 1041 is obtained based on the density value for each of the reading areas 22Y, 22B, 22C, and 22M, but the present invention is not limited to this. For example, the drive voltage value to the print head 1041 may be measured each time it is corrected, and density information of the print head 1041 may be obtained based on the drive voltage value to the print head 1041.

[0040] When ink droplets are ejected from the multiple nozzles 1042 of each print head 1041 in response to the same drive voltage, it is desirable that the ejection volume of the ink droplets be uniform. However, variations in temperature within the print head 1041, variations in the characteristics of the printing elements of the print head 1041, etc. may cause variations in the ejection volume of the ink droplets.

[0041] If there is variation in the amount of ink droplets ejected among the multiple nozzles 1042, density unevenness occurs in the multiple reading areas 22Y, 22B, 22C, and 22M aligned in the main scanning direction Dm. The occurrence of density unevenness reduces the quality of the formed image.

[0042] This density unevenness can be addressed by partially changing the drive voltage, which is a drive condition, within the print head 1041. However, if recycled paper, old paper, or the back side of a printed sheet (so-called backing paper), which vary in quality, is used as the sheet P, the density unevenness in the check patterns 21Y, 21B, 21C, and 21M may vary (be unstable) for each sheet P. As a result, the density information of the print head 1041 acquired from the check patterns 21Y, 21B, 21C, and 21M may also vary for each sheet P. As a result, even if the drive conditions of the print head 1041 are corrected, the density unevenness may not be resolved, and image quality may deteriorate.

[0043] In this embodiment, a correction mode can be executed to correct the drive conditions of the print head 1041, and the drive conditions of the print head 1041 are repeatedly corrected until the calculated density information of the print head 1041 becomes equal to or less than a predetermined threshold value. This makes it possible to suppress density unevenness from occurring when the normal image formation mode is executed.

[0044] Furthermore, when the drive conditions of the print head 1041 are corrected a predetermined number of times, the control unit 107 determines whether the density information of the print head 1041 has converged toward a predetermined value each time the drive conditions of the print head 1041 are corrected. At this time, if the density information of the print head 1041 has not converged toward the predetermined value, the control unit 107 determines that the reason why density unevenness has not been resolved even when the drive conditions of the print head 1041 have been repeatedly corrected is because there is variation in the quality of the sheet P.

[0045] If it is determined that the cause is variation in the quality of the sheet P, the control unit 107 changes the threshold value. At this time, the changed threshold value is, for example, a threshold value that corresponds to the case where there is variation in the quality of the sheet P, and is stored in advance in the storage unit. The control unit 107 (determination unit 1077) determines whether density unevenness has occurred in a part of the check chart 20 using the changed threshold value, and determines whether density unevenness has occurred in a part of the check chart 20. If the density information of the print head 1041 exceeds the changed threshold value, the determination unit 1077 determines that density unevenness has occurred in a part of the check chart 20 due to a cause other than variation in the quality of the sheet P.

[0046] On the other hand, if the density information of the print head 1041 is equal to or less than the changed threshold value, the determination unit 1077 determines that density unevenness has occurred in part of the check chart 20 due to variations in the quality of the sheet P, and that the drive conditions of the print head 1041 have been correctly corrected by the immediately preceding correction. Therefore, the drive conditions of the print head 1041 can be corrected while taking into consideration variations in the quality of the sheet P. This makes it possible to suppress the occurrence of density unevenness while dealing with variations in the quality of the sheet P when performing normal image formation mode, and reduce degradation in the quality of the formed image.

[0047] It is preferable to display on the display unit 2 that the threshold value has been changed, so that the user can recognize that correction is being performed to eliminate density unevenness when the normal image formation mode is being executed.

[0048] On the other hand, when the density information of the recording head 1041 is converging toward a predetermined value, the control unit 107 determines that the reason why the density unevenness is not eliminated even when the driving conditions of the recording head 1041 are repeatedly corrected is not due to variations in the quality of the sheet P.

[0049] In this case, even if the drive conditions of the print head 1041 have been corrected more than the predetermined number of times, the density unevenness has not been eliminated, so execution of the correction mode is temporarily stopped. By limiting the number of corrections of the drive conditions of the print head 1041 to a predetermined number, the execution time of the correction mode can be limited, thereby reducing the user's waiting time. Note that when execution of the correction mode is stopped, it is preferable to display an error message on the display unit 2. This allows the user to recognize that density unevenness will occur.

[0050] FIG. 5 is a flowchart showing an example of execution of the correction mode of the inkjet recording apparatus 100 of the first embodiment. In this embodiment, the correction mode is executed when the cassette CA is installed in the apparatus main body 101. As a result, when the sheet P is replaced, the driving conditions of the recording head 1041 are corrected according to the type of sheet P. Therefore, when the image formation mode is executed, it is possible to suppress the occurrence of density unevenness and reduce degradation in the quality of the formed image. The correction mode may also be executed by the user inputting through the operation unit 3.

[0051] When the correction mode starts, the drive conditions of the print head 104 are set (step S1). If the drive conditions of the print head 1041 have never been corrected, the drive conditions of the print head 104 are returned to the initial settings. The initial setting drive conditions are, for example, all of the drive voltages to the print heads 1041 being the same.

[0052] Next, a check chart 20 for density measurement is recorded on a sheet P based on the driving conditions of the recording head 104 set in step S1 (step S2). Specifically, image data of the check chart 20 is sent to the image processing unit 1071, and recording data of the image data is generated. The discharge control unit 1072 controls the recording head 1041 based on the recording data to record the check chart 20 on the sheet P. At this time, the driving voltage to the recording head 1041 is controlled based on the driving conditions of the recording head 1041 set in step S1. The image data of the check chart 20 is stored in advance in a storage unit or the like within the inkjet recording apparatus 100.

[0053] Next, the check chart 20 recorded on the sheet P is optically read by the image reading unit 4 (step S3). Specifically, the check chart 20 is read by a plurality of detection elements 41 arranged along the main scanning direction Dm. The image reading unit 4 generates image data corresponding to the read image and transmits the image data to the density information acquisition unit 1075.

[0054] The density information acquisition unit 1075 acquires density information of the recording head 1041 based on the image data of the check chart 20 received from the image reading unit 4. The determination unit 1077 determines the density information of the recording head 1041 acquired by the density information acquisition unit 1075 using a threshold value stored in advance in a storage unit (step S4). This makes it possible to determine whether density unevenness has occurred in a part of the check chart 20. If the determination unit 1077 determines that the density information of the recording head 1041 exceeds the threshold value and that density unevenness has occurred in a part of the check chart 20 (NO in step S4), it identifies the nozzle 1042 that is causing the density unevenness from the result of the determination and proceeds to step S5.

[0055] On the other hand, if the determination unit 1077 determines that the density information of the print head 1041 is equal to or less than the threshold value and that no density unevenness has occurred in the check chart 20 (YES in step S4), the process proceeds to step S9. In step S9, the drive conditions of the print head 104 set in the immediately preceding step S1 are set as the drive conditions of the print head 104 in the normal image formation mode, and the correction mode ends.

[0056] In step S4, fixed threshold values ​​stored in advance in a storage unit or the like are used to detect density unevenness. Threshold values ​​are stored in advance for each of the colors yellow, black, cyan, and magenta.

[0057] In step S5, it is determined whether or not steps S1 to S4 have been repeated a predetermined maximum number of times while the correction mode is being executed. In this embodiment, the maximum number of times steps S1 to S4 are repeated is preset to five. As a result, if steps S1 to S4 have been repeated five times, the process proceeds to step S6 (YES in step S5). Note that the maximum number of times steps S1 to S4 are repeated is set to five in this embodiment, but is not limited to this.

[0058] On the other hand, if steps S1 to S4 have been repeated less than five times, the process returns to step S1 and steps S1 to S4 are executed again. At this time, in step S1, the drive conditions of the print head 1041 are corrected based on the density information of the print head 1041 acquired in the immediately preceding step S4, and the corrected drive conditions of the print head 104 are set.

[0059] In step S2, based on the driving conditions of the recording head 1041 corrected in step S1, a check chart 20 for density measurement is recorded on a sheet P. At this time, a new sheet P is supplied every time steps S1 to S4 are repeated.

[0060] By repeating steps S1 to S4, density variations caused by variations in temperature within the print head 1041, variations in the characteristics of the print elements of the print head 1041, and the like can be corrected with high precision.

[0061] In step S6, it is determined whether the density information of the print head 1041 has converged toward a predetermined value each time steps S1 to S4 are repeated and the drive conditions of the print head 1041 are corrected.

[0062] 6 to 8 are graphs showing the relationship between the number of times the drive conditions of the recording head 104 are corrected and the density value, and show the relationship between the number of times the drive conditions of the recording head 104 are corrected and the density value in any of the reading areas 22Y, 22B, 22C, and 22M where density unevenness has occurred. As shown in FIG. 6, the density value of the check chart 20 after correction alternates between being dark and light on either side of the convergence value S, and if it does not converge to the convergence value S (NO in step S6), the process proceeds to step S7.

[0063] At this time, the density information of the recording head 1041 does not converge toward a predetermined value, and the control unit 107 determines that the density unevenness is not eliminated even after repeatedly correcting the driving conditions of the recording head 1041, because there is variation in the quality of the sheet P.

[0064] On the other hand, as shown in FIGS. 7 and 8, if the density value of the check chart 20 after correction has converged to the convergence value S (YES in step S6), the process proceeds to step S10.

[0065] At this time, the density information of the recording head 1041 has converged toward a predetermined value, and the control unit 107 determines that the reason the density unevenness remains even after repeated correction of the drive conditions of the recording head 1041 is not due to variations in the quality of the sheet P. In step S10, an error message is displayed on the display unit 2, and execution of the correction mode is stopped.

[0066] In step S7, the threshold value is changed and reset, and the process proceeds to step S8. The changed threshold value is a threshold value that corresponds to the case where there is variation in the quality of the sheet P, as described above, and is stored in advance in the storage unit.

[0067] In step S8, the determination unit 1077 determines whether the density information of the recording head 1041 acquired in the immediately preceding step S4 is equal to or less than the changed threshold value. This makes it possible to determine whether density unevenness has occurred in a part of the check chart 20 based on the changed threshold value. If the determination unit 1077 determines that the density information of the recording head 1041 exceeds the threshold value and that density unevenness has occurred in a part of the check chart 20 (NO in step S8), the process proceeds to step S10, where an error message is displayed on the display unit 2 and execution of the correction mode is stopped.

[0068] On the other hand, in step S8, if the density information of the recording head 1041 is below the changed threshold value (YES in step S8), the judgment unit 1077 judges that density unevenness has occurred in the check chart 20 due to variations in the quality of the sheet P, and proceeds to step S9.

[0069] In step S9, the drive conditions of the recording head 104 set in the immediately preceding step S1 are set as the drive conditions of the recording head 104 in the normal image formation mode, and the correction mode is terminated. As a result, when the next image formation mode is executed, it is possible to suppress the occurrence of density unevenness while dealing with variations in the quality of the sheet P, and reduce degradation in the quality of the formed image.

[0070] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these, and various modifications can be made without departing from the spirit of the invention.

[0071] For example, in this embodiment, the image reading unit 4 is included in the inkjet recording apparatus 100, but the image reading unit 4 may be a separate device that is different from the inkjet recording apparatus 100. [Industrial Applicability]

[0072] The present invention can be used in maintenance such as detecting density unevenness in the nozzles of an inkjet recording device. [Explanation of symbols]

[0073] 1 Density unevenness detection unit 2 Display section 3 Control section 4 Image reading unit 20 Check Chart 21Y, 21B, 21C, 21M check pattern 22Y, 22B, 22C, 22M reading area 41 Detector element 100 Inkjet recording device 101 Main Unit 101 Device body 102 Sheet supply unit 103 Sheet transport unit 104 Recording section 104 Recording head 105 Drying section 106 Sheet discharge section 107 Control Unit 1031 First belt conveyor 1032 Second belt conveyor 1033 Branch 1034 Reversing conveying section 1041 Recording head 1041B, 1041C, 1041M, 1041Y recording head 1042 nozzle 1071 Image Processing Unit 1072 Discharge control section 1073 Correction Unit 1075 Concentration information acquisition unit 1077 Judgment section CA cassette Dm Main scanning direction Ds Sub-scanning direction P-sheet S convergence value

Claims

1. a recording unit that ejects ink from a plurality of nozzles of a plurality of recording heads to record an image on a sheet; an image reading unit that reads the density of the image recorded on the sheet; a control unit that controls the recording unit and the image reading unit, the control unit is capable of executing a correction mode for correcting a driving condition of the recording head during execution of a normal image forming mode, When the correction mode is executed, the control unit causes the image reading unit to read a check chart for density measurement recorded on the sheet by the recording unit, acquires density information of the recording head, and repeatedly corrects the drive conditions of the recording head until the acquired density information of the recording head becomes equal to or less than a predetermined threshold value; When the drive conditions of the recording head are corrected a predetermined number of times, the inkjet recording device determines whether the density information of the recording head has converged toward a predetermined value each time the drive conditions of the recording head are corrected, and changes the threshold value if the density information of the recording head has not converged toward the predetermined value.

2. 2. The inkjet recording apparatus according to claim 1, wherein the control unit stops execution of the correction mode when the density information of the recording head is converging toward a predetermined value.

3. a display unit that displays information about the recording unit, The inkjet recording apparatus according to claim 1 , wherein the control unit displays on the display unit that the threshold value has been changed.

4. a display unit that displays information about the recording unit, The inkjet recording apparatus according to claim 2 , wherein the control unit displays an error message on the display unit when the execution of the correction mode is stopped.

5. 3. The inkjet recording apparatus according to claim 1, wherein the control unit corrects the drive conditions of the recording head by adjusting a drive voltage of the recording head.

6. a sheet supply unit including a cassette for storing the sheets; 3. The inkjet recording apparatus according to claim 1, wherein the control unit executes the correction mode when the cassette is attached to a main body of the apparatus including the recording unit.

Images